In invasive breast cancers, we find very high rates of loss of heterozygosity (LOH) for markers around the D14S302 locus on chromosome 14q, suggesting the presence of a nearby tumor suppressor gene. However, at the adjacent marker D14S62, we find high LOH in invasive primary breast cancers but virtually none in nodal or distant metastases, or in breast cancer cell lines derived from metastases, indicating that an additional gene essential for metastasis (e.g., a cell adhesion molecule or protease) must reside quite close to this marker. Our hypothesis is that the deletion of one copy of this gene prevents or seriously retards the process of metastatic spread of breast cancer. In a very small preliminary study, we found that breast cancers with D14S62 LOH were much more likely to be node-negative than node-positive, and much less likely to recur even if node-positive. To further explore the genetic basis and clinical significance of these provocative observations, we therefore propose: (1) To better define the position of the new metastasis gene and increase the number of patients who are genetically informative, by testing additional highly polymorphic 14q markers near D14S62 in 70 node-negative and node- positive breast cancers; (2) To assess the prognostic potential of LOH at these markers by examining microdissected breast tumor biopsy specimens from an additional 167 patients with extended clinical follow up and comparing the D14S62 region LOH profile with nodal status and incidence of recurrent cancer; and (3) to identify candidate cDNAs for new metastasis gene by carrying out high resolution mapping. Once the locus is defined, exon trapping and direct cDNA selection will identify candidate transcripts for the metastasis gene. Candidates with assessed for their pattern of expression and function in breast cancer cells. These studies have the potential to provide a genetic or immuohistorchemical test that would aid in predicting recurrence and therefore in treating breast cancer patients. Understanding the mechanism of action of our metastasis gene could also lead to therapies to interfere with the process of metastasis in patients identified at high risk of metastatic spread.